The organic light emitting diode (OLED) display apparatus is recognized by the industry as the most promising display device due to many advantages such as self-luminousness, low driving voltage, high luminous efficiency, short response time, high resolution and contrast, viewing angle nearly 180°, wide temperature range, and capability of achieving the flexible display and large-area panchromatic display.
According to the driving mode, OLED can be classified into a passive matrix OLED (PMOLED) and an active matrix OLED (AMOLED), i.e., direct addressing and thin film transistor matrix addressing. Among them, AMOLED has a matrix arrangement of pixels, belonging to the active display type; due to the high luminous efficiency, AMOLED is usually used for high-definition large-size display apparatus.
The OLED generally includes a substrate, an anode disposed on the substrate, a hole injection layer disposed on the anode, a hole transport layer disposed on the hole injection layer, and a light emitting layer disposed on the hole transport layer, an electron transport layer on the light emitting layer, and a cathode disposed on the electron transport layer. The principle of light-emitting OLED display devices is that emit light by carrier injection and recombination under an electric field. Specifically, an OLED display device generally adopts an ITO pixel electrode and a metal electrode as an anode and a cathode of the device respectively. Under a certain voltage, electrons and holes are injected from the cathode and the anode into the electron transport layer and the hole transport layer respectively; the electrons and holes migrate to the light emitting layer through the electron transport layer and the hole transport layer respectively, and meet in the light emitting layer to form excitons to excite the light-emitting molecules, which emit visible light through radiation relaxation.
The most common manufacturing method of the OLED device is that preparing a hole injection layer, a hole transport layer, and a light emitting layer by ink-jet printing and preparing an electron transport layer and a cathode by vacuum thermal evaporation; due to the high cost of the vacuum thermal evaporation, a high production cost of the OLED device is caused, so a large-scale commercialization of the OLED device is limited. The ink-jet printing method uses a plurality of nozzles to drop the ink of the functional material into a predetermined pixel area, and then the desired film is obtained by drying. The method has the advantages of high material utilization and the like, and is a key technology for solving the problem of the display cost of a large-size OLED. However, due to the mutual miscibility between the adjacent printing ink layers, and the materials of the electron transport layer and the cathode are mostly the evaporation materials, it is very difficult to achieve an all-solution-process OLED device.